1. Field of the Invention
The present invention relates to a visual inspection technology using image processing, and more particularly, to a surface inspecting apparatus for detecting a spot or contaminant on a surface of an object, regardless of the intensity gradient on the surface and pattern presence on the surface, by taking the surface image of the object to use internal symmetry feature of the spot or contaminant and a method therefor. The present invention further relates to a computer-readable recording medium for storing a program for implementing the above method.
2. Description of the Prior Art
Conventionally, in order to detect a spot on a surface of an object, there are several methods, such as a spot detecting method using a binary quantization scheme for an input image and another spot detecting method using, sequentially, smoothing space filtering scheme where a value of a reference pixel is given by an average of the intensity value of the reference pixel and intensity values of adjacent pixels around the reference pixel and space filtering scheme exhibiting the difference between the intensity value of the reference pixel and the intensity values of the adjacent pixels around the reference pixel.
However, since the conventional spot detecting methods as described above detect the spots based on the difference between the intensity value of the reference pixel and the intensity values of the adjacent pixels around the reference pixels, they are applicable to the surface which has uniform intensity thereon and has no pattern in the background thereof. That is, the conventional methods can not be applied when the intensity of the surface to be inspected is non-uniform or there is pattern on the surface to be inspected.
It is, therefore, a primary object of the invention to provide a surface inspecting apparatus for detecting a spot or contaminant even if the surface has non-uniform intensity thereon or it has pattern thereon, a method therefor and a computer-readable recording medium for storing a program for implementing the method.
That is, the object of the present invention is to provide a surface inspecting apparatus capable of, differing from detecting spots based on the difference between intensity value of a reference pixel and the intensity values of the adjacent pixels around the reference pixels, detecting a spot or contaminant when the intensity of the surface to be inspected is non-uniform or there is pattern on the surface to be inspected by exhibiting the internal symmetry feature of the spot or contaminant by using the magnitude of the intensity gradient and the orientation of the intensity gradient of input pixels of a surface image, a method therefor and a computer-readable recording medium for storing the program for realizing the method.
In accordance with one aspect of the present invention, there is provided a surface inspecting apparatus comprising an image achieving unit for achieving an image of a surface of an object; and a controller for providing the symmetry feature of the spot or contaminant by using the magnitude of the intensity gradient and the orientation of the intensity gradient for each pixel of the achieved surface image to thereby detect a spot or contaminant on the surface, wherein the controller detects the spot or contaminant by using a symmetry magnitude map formed by the magnitude of the intensity gradient and the orientation of the intensity gradient of each pixel, after achieving the magnitude of the intensity gradient and the orientation of the intensity gradient by using a gradient operator on the achieved surface image, wherein the symmetry magnitude map provides the internal symmetry feature of the spot or contaminant.
In accordance with another aspect of the present invention, there is provided a method for inspecting a surface of an object, for use in a surface inspecting apparatus, comprising the steps of: first achieving the magnitude of the intensity gradient and the orientation of the intensity gradient of each pixel in the image of the surface by using a gradient operator; second achieving a symmetry magnitude map by using the magnitude of the intensity gradient and the orientation of the intensity gradient of each pixel, wherein the symmetry magnitude map exhibits the internal symmetry feature of a spot or contaminant on the surface; and detecting the spot or contaminant by using the symmetry magnitude map.
In accordance with still another aspect of the present invention, there is provided a computer-readable recording medium for storing a program, the program implementing in an apparatus having a large capability processor for inspecting a surface of an object, first function for achieving the magnitude of the intensity gradient and the orientation of the intensity gradient for each pixel of the image of the surface by using a gradient operator on the image; second function for achieving symmetry magnitude map exhibiting symmetry feature of a spot or contaminant by using the magnitude of the intensity gradient and the orientation of the intensity gradient; and third function for detecting the spot or contaminant by using the symmetry magnitude map.